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Monday, 17 June 2013

Our group of three scientists (myself, Christina Thiele, and Rebekah Newstead) are here on-board the RRS James Cook to collect information on the community structure of mesozooplankton (zooplankton in between 0.2- 2 mm) from the surface through the twilight zone to 1000m. We are also interested in how zooplankton may be influencing the transport of carbon through the twilight zone and into the deep sea where it can stay for thousands of years.

One of the ways that zooplankton can influence this is by feeding on smaller plankton and marine snow and packaging them into faecal pellets which can sink faster than the smaller particles. Yes, pretty much every animal in the ocean poops, and zooplankton produce a lot of poop! Zooplankton also come in many shapes and sizes and so does their poop. Understanding how these characteristics differ from region to region can help us learn more about carbon flux and transformations of marine snow throughout the oceans.

The pelagic harpacticoid copepod Microsotella sp.
seen under the microscope.

Species such as salps produce really big pellets which sink close to 1000 m per day. Large amphipods, currently common at the Twilight station also produce large, quickly sinking pellets. Some other taxonomic groups produce tiny pellets which may degrade before they sink too far. For example harpacticoid copepods (an order of copepods) most of which are benthic. But when found living in the water column like the genus Microsotella sp., they colonise particles such as, you guessed it, poop.

Another one of our tasks was to measure rates of faecal pellet production by some of the dominant mesozooplankton in the region. We are specifically looking at the larger species that will be producing faecal pellets which may be transported out of the surface waters. This can be done by either passive sinking of large pellets or a more active transport during a zooplankton’s daily migration from the surface at night (where they feed) to the deeper and darker twilight zone at dawn (where they stay until dusk to avoid visual predators). On their way, they produce faecal pellets.

These pellets have within them the remnants of past meals and are an important mechanism for the transport of carbon to the deep sea. The three groups we chose to look at here on the cruise were salps, the large amphipod Themisto, and the daily migrating copepod Pleuromamma. We collect them, put them in special “poop trap” jars that will separate out the poop (because they like to eat the poop too), and count how many pellets they produce per hour.

By looking at the community structure as well as the faecal pellet production rate we can calculate potential carbon fluxes for some of the zooplankton species. Then we can compare these rates to what we find in the sediment traps and see which species are contributing the most to carbon transport through the twilight zone. This part of our project will be highly collaborative as we all share our data to create an interesting story about poop and marine snow in the twilight zone.

Sunday, 16 June 2013

The traditional way to collect the small, drifting animals in the sea that are called zooplankton is to use plankton nets, and then analyze the tiny organisms under microscopes in the lab. That way you get a close-up view of the plankton, you can watch their movements (unless you preserve them at once!) and observe them from all sides. This makes it easy to determine the species of these animals, which range in size from less than a millimeter to a few centimeters. Unfortunately, many of the fragile forms are destroyed in the sampling process, and exist only as fragments in your sample.

The Video Plankton Recorder (VPR) is a complimentary tool to the plankton nets and marine snow collecting systems used during this cruise. It is an underwater digital video camera with a macro lens and a flashing strobe for illumination, which is lowered into the water and towed up and down several times. It takes about 20 little pictures per second, and can be towed at a speed of a meter per second or more. The VPR lets you observe images of undisturbed, living plankton and particles (“marine snow”) in the water column and knowing exactly at what depth and temperature individual plankton are observed.

Here are some images of plankton collected with the VPR during this cruise.

Appendicularians have a spinal cord, which make them our closest relatives among the invertebrates. They look a little like tadpole larvae, and are therefore sometimes called Larvaceans. Appendicularians build their own intricate “houses” with feeding nets to collect the smallest particles in the sea. However, these animals only live in their houses for a few hours before leaving them and building another. The discarded houses collapse and form a large part of the marine snow.

Copepods are one of the most abundant and wide spread animals groups in the ocean and also some of the most numerous animals on Earth. You can find them everywhere, eating phytoplankton, other copepods and even marine snow! Their poo is also a part of the marine snow.

Siphonophores are strange kinds of jellyfish. living in colonies where each individual has its specialized job. Some have tentacles to catch and sedate prey, others digest it, and others again help the whole colony swim and float. You may have heard of the infamous siphonophore “Portugese man-of-war” - but most are quite harmless to humans.

Powering up now for the #Planktonpoo Twitterfest on Monday (1200h GMT) with a great team on board the RRS James Cook to respond. This will be Morten Iversen from Bremen with insights into particle degradation, Stephanie Wilson from Bangor working on plankton faecal characterisation and me from NOC, Southampton who has expertise in particle sinking. On shore there will also be a team of experts eager to communicate their work, so I think this should be a really good event. We have in fact finished the research programme at sea and are now steaming back towards Glasgow, where we started off just over two weeks ago. By Monday we will be within sight of land after some highly successful observations and experiments.

As we have reported before, this expedition has been over the Porcupine Abyssal Plain which lies around 350 miles southwest of Ireland (water depth 4800m), an area we like to think of as “typical” of the open ocean between the icy polar regions and the tropics. There is still a load of work to do, analysing the samples we have collected and processing the mass of data already in the bag, much of it to do with particles in the ocean, both dead and alive. But without a doubt there will be some really important things to say over the coming months when the processing has be done and the dots between the different studies conducted, have been connected.

So what do we actually mean by “Plankton poo”? Well, this faecal matter is just one of several types of particle which sink under their own weight and thus transport carbon from the upper parts of the ocean down thought the twilight zone into the ocean's interior. But it is not only the poo of small planktonic animals that sink to the deep ocean. A more general term for such sinking particles is Marine Snow. It describes aggregations of all sorts of dead organic material and includes not only faecal material (plankton poo) but also aggregations of dead phytoplankton cells (microscopic plants), dead zooplankton, plankton moults and some inorganic minerals scavenged for good measure. Stuck together with a gluey matrix they can sink at rates between 100 and 1000m per day. On their way down they sometimes get caught and eaten by zooplankton before they arrive at the bottom of the ocean where they provide nourishment for other animals living on the seafloor.

By Richard Lampitt (Chief Scientist on James Cook cruise “Down to the Twilight Zone”)

Saturday, 15 June 2013

Around fifty hungry mouths have to be fed three times a day, seven days a week on the RRS James Cook. So Peter Lynch, the head chief and his four man crew have to work from 6 o'clock in the morning to 7 o'clock at night to keep the crew, technicians and scientists happy.

As you can imagine, different from a kitchen on land this one has to be equipped for rough weather at sea. To keep the galley functional in a storm the hobs have big bars on them to prevent pans falling off, and cloths and gripping mats prevent food from rolling about.

Lunch is served

For breakfast there is of course, Full English Breakfast; bacon & eggs, sausages, grilled tomatoes, hash browns, black pudding (aka blood sausage) and toast. In case you are looking for something a bit more 'continental', croissants and fruits as well as cereals are also available.
For lunch and dinner, a diversity of international and classical English dishes is served. For example yesterday we had Yorkshire Pudding. For all you non-British readers, this has nothing to do with a sweet pudding, but rather resembles a savoury muffin-lookalike croissant type of bun which is served with gravy, quite tasty though. For dinner, desert is available as well.

As on all research vessels the time for eating is kept fairly short for practical reasons, so you better be on time to enjoy your meal. Since people are working 24/7 on the ship it is sometimes impossible to make it to breakfast, lunch or dinner. In this case the galley staff are happy to put a dish aside for you. And in case you get hungry in between meals there are always leftovers from the previous meals (and a microwave to heat it) as well as toast and fruits available.

This cruise only lasts for three weeks, so we are lucky to be served fresh fruits and vegetables throughout the whole expedition. For longer ones though, you would be able to see the suggestion of durability of food. Even though vegetables are kept in room-size fridges (see picture) after approximately four weeks they reach their limit of durability, while other and fresh food like cabbage last a bit longer. The meat is stored in walk-in freezers (at -20C) so that it can be available even throughout longer journeys.

Friday, 14 June 2013

The spout of a whale is one of the iconic images of the open sea, and it is one we have been lucky enough to see several times on this cruise. Such a sight is fleeting, however. The majority of a whale’s life is spent below the surface, with sperm whales known to dive as deep as 3km down into the ocean.

This makes it very difficult to do something as seemingly simple as to count how many whales there are in the sea. Given the vast expanses of the ocean, covering over two thirds of the Earth, even when they do surface it is very unlikely a ship will be there to see them and take note. So, if we want to study whales, we need a way to see underwater.

Two whales, one showing a flipper

Unfortunately, sunlight penetrates only a very short distance through water. However, sound can travel great distances. This is how whales themselves communicate, so maybe the thing to do is simply to listen in. To do this, the boffins at the Sea Mammal Research Unit of the University of St Andrews have been developing very sensitive underwater listening devices, called hydrophones. The ocean is a surprisingly noisy place though. Our current home, RRS James Cook, itself provides a constant background of engine noise that makes listening for distant whales like trying to hear a conversation in a crowded room. What is needed is a quiet place to put the hydrophone to eavesdrop on the whales. Cue Pelagra, the floating sediment traps we have been using to collect and study marine snow. These may provide an ideal platform. They hover silently on their own, hundreds of metres down in the water, away from waves and boats.

SMRU have very kindly lent us one of their detectors which, even now, is strapped to the side of Pelagra P8, heading westwards in an orderly manner, 200m below the surface. Tomorrow morning, P8 is due to pop up and be collected. Hopefully, we will then be lucky enough to hear whale sounds as well as see them.

By Adrian Martin

P.S.: The PELAGRA P8 has been recovered successfully this morning at around 06:00. And we were fortunate enough to find a short recording of a whale calling. (Opens new window - please close to return to this page)

More than two-thirds of the Earth’s surface is covered by Oceans, and there are huge quantities of these tiny plants. Large enough in fact to make up approximately half of the global biosphere production!

Being the primary elements of the food chain they affect the abundance and diversity of marine organisms throughout the food-chain and play a major role in marine ecosystem functioning and fishery yields. Since they are plants they take up carbon dioxide, and hence, they are a major sink for the carbon dioxide in the atmosphere.

Considering their importance to the carbon cycle, it is vitally important and indeed our duty, to study them. That means we need to estimate their quantity and presence in the different regions of the ocean. To do so we have to ask some big questions. For example how does their concentration vary throughout the water column? How does their size vary with depth and geographic location? Which species dominate with the seasons of the year and on decadal timescales?

To answer these questions we need a better understanding of the different factors that affect phytoplankton, how are marine organisms affected by human activities and in turn how do they influence our own environment. Confused? These are not trivial questions, even for scientists.

On this cruise I am trying to answer a few of these questions in relation to the PAP site. For example, how many of these plants are present in these waters? How does their quantity and size vary as we enter the Twilight Zone?
Now, I know you may wonder how we measure plants not even visible to the naked eye. Well, here's the simple answer; every plant on Earth contains the pigment 'chlorophyll a.'

The deployment of the CTD

Once we recover water samples from the Twilight Zone using the CTD Rosette (image right), we use an optical instrument that bombards the chlorophyll with a particular wavelength to make it fluoresce or glow, and the amount of fluorescence is a direct proxy of the amount of chlorophyll, and therefore phytoplankton the seawater contains.

Once that is done, we can move to answering some of the more complex questions.

A project of

About the Expedition

Close your eyes and take a deep imaginary dive to the ocean abyss, preferably in early summer. No matter how hot it is where you might be, the abyss at this time is probably experiencing a short-lived blizzard of marine snow.

The deep sea has its own climate it would appear, and a dense storm of fluffy particles coats the seabed, only to be gobbled up by deep sea creatures soon after.

Technological advances allow multiple ways for observing the planet and its oceans from the comfort of an armchair and the click of a button, but understanding marine snow and how it links to the climate we are more familiar with, still requires ocean-going expeditions, and occasionally getting wet.